The handling of fine particles with a high surface area and low density has proven to be particularly troublesome in those industries which handle such material. One particular problem in fine particle handling is the providing of a system that is essentially dust-free so as to maintain a safe working environment while also providing a quick, easy and relatively inexpensive handling system. In addition, any time there is a dust problem in the working environment, there is also an increased chance of contamination of other products. The amount of dust which is produced in the working environment is related in some respects with the manner in which the fine particles are received by the intended users. Some recipients of fine particles rely on silos or storage rooms which are capable of handling large volumes of material. With such storage facilities, bulk delivery is typically the most economical and often features road or rail-born silo vehicles with pneumatic pumps that can pump the material from the silo vehicle directly to the storage facility. Hence, this system is very effective in maintaining a relatively dust-free working environment. However, not all facilities have the necessary equipment or storage space for receipt of a bulk delivery while other facilities do not use a sufficient volume of the fine particle material to warrant the expense of a bulk delivery receiving system.
For low volume users of fine particles or for recipients which have little storage space, delivery of the fine particles by way of paper sacks stacked on pallets is often preferred. However, the potential for dust creation is high when dealing with individual bags as the opening and disposal of each bag has a tendency to release dust into the environment. While there are automated assemblies for opening, emptying and discarding bags, this equipment is very expensive and thus often not economically plausible for many recipients.
Many customers or recipients prefer semi-bulk delivery as it avoids the high labor requirements associated with handling a plurality of individual paper sacks or because they use an amount of the particle material which falls between the extremes of bulk delivery and paper sack delivery. In an effort to satisfy the requirements of these intermediate users, various semi-bulk containers have been introduced. For example, a container-formed of reinforced lined fabric has been utilized. This flexible container is suspended and typically discharged by the opening of an integral nozzle forming part of the flexible container into an inner port of a further processing or delivering system.
The use of a flexible intermediate bulk container can, however, present some problems with respect to escape of particles during the release of the particles to the downstream processing or delivering system. In addition, before the empty bag can be discarded, it has to be folded to a size which may be easily handled. The folding and handling of the large bag can lead to a large generation of dust in the environment, especially in light of the fact that the particles often stick to the side of the container due to the static charges which develop during emptying. The requirement for disposing of the intermediate bulk containers also creates a large waste disposal problem which is environmentally undesirable.
Attempts to reuse the intermediate or semi-bulk containers present numerous problems such as contamination problems and increased dust creation.
The industry has also utilized folding cardboard boxes as semi-bulk containers and the like, which are disposed in the same manner as the flexible reinforced fabric bulk containers. Some of these disposable cardboard boxes use an intermediate layer of plastic lining and an inner cardboard sleeve. Removal of the particles in these boxes includes the use of a shower head type nozzle which fluidizes and draws the particles out once the box and liner are opened for receipt of the nozzle head. As with the reinforced fabric semi-bulk containers, there is a great deal of undesirable dust creation and waste disposal requirements associated with collapsible cardboard boxes of this type. The industry has also used permanent, refillable containers, but this adds to the cleaning and shipping weight costs and thus has not been used extensively in the industry.
The requirement for a dust-free working environment is mandated in many countries by way of regulations which fix the maximum dust concentration that can exist in the work environment. The maximum dust concentration value is determined, in part, on the perceived health risk associated with a particular fine particle material. These regulations typically set a limit value on the weight of fine particle material per given volume of air or upon the number of particles per given volume of air. For example, although synthetic amorphous silicas have not been found to be harmful to the lungs to date, these substances are included in the list of materials which have been assigned a maximum concentration value at the work place. In the Federal Republic of Germany, for example, the maximum synthetic silica concentration is set at 4 mg/m.sup.3. It is thus imperative that the fine particle handling process and any later disposal requirements be of a type which avoids the introduction of dust into the environment.
Many fine particles also produce tremendous electrostatic charges when being conveyed, particularly at very high speeds. Hazards connected with static charges of this nature, e.g. flying sparks have resulted in the introduction of grounding or earthing systems in the piping systems used to transport synthetic silicas from storage rooms or silos. The static charges which develop also cause particles to stick to the interior of the containers which is not only a loss of material, but also creates a higher potential for dust production in the work place during container disposal.